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This invention relates to fuel systems for internal combustion engines and more particularly to a fuel injection system whereby two distinct fuels are used, either alternatively or simultaneously.
With ever more stringent emissions regulations, the use of alternative gaseous fuels for operating internal combustion engines has become increasingly attractive. The more commonly used gaseous fuels are compressed natural gas (CNG) and liquefied petroleum gas (LPG). These gases can burn cleaner than gasoline and the cost per unit of energy is lower.
A majority of the end users are specifically requesting dual fuel systems, capable to run on gasoline or a gaseous fuel, such as CNG or LPG. While factory installed gaseous or dual fuel systems are available today, in many cases, the gaseous fuel system is still a retrofit complementing the original gasoline fuel system.
Another possible application for a dual fuel system is the use of methanol fuel as an alternative to, or in combination with, gasoline. In some countries, methanol is readily available and cost-effective. The use of a mixture of gasoline and methanol has certain advantages but it is difficult to implement, because the two liquids do not mix well.
The last decade has witnessed the migration of the automotive engine fuel system from carburetors to port fuel injection, using one fuel-metering device, in the form of a fuel injector, for each engine cylinder. This migration has been driven by the numerous drawbacks associated with central mixture preparation. Carburetors create a significant restriction in the intake air path, thereby impairing the volumetric efficiency of the engine. Furthermore, central mixture preparation entails air-fuel ratio maldistribution among the different cylinders of the engine, with negative consequences on the exhaust emissions.
Although virtually all of the modern automotive gasoline fuel systems are of the port fuel injection type, many of the dual fuel, liquid and gas, systems still resort to a centrally located airxe2x80x94fuel mixing device for supply and metering of the gaseous fuel. This central mixture preparation device most often consists of some variety of a carburetor. A few systems use central fuel injection instead.
A lot of effort has been made in the last few years to develop advanced port injection gaseous fuel systems. Gaseous variants of the gasoline port fuel injection have been developed for dedicated, gas only, applications.
Design of simple and reliable dual fuel port injection systems has been less successful. Most prior art dual fuel systems which do utilize injectors for both fuels use two separate injectors, one for each of the fuels (such as described by U.S. Pat. No. 5,755,211xe2x80x94Koch, or U.S. Pat. No. 5,713,336xe2x80x94King et al). Some of the disadvantages of this solution are:
Two separate fuel rails are used, cluttering the system and complicating installation.
Doubles the number of injectors in the system, compared to a single fuel application.
A second electronic control unit (ECU) is required to drive the gaseous fuel sub-system.
Attempts have been made to integrate the delivery of both fuels into one single injector device (U.S. Pat. No. 5,887,799xe2x80x94Smith). Some of the disadvantages of the solution proposed by the author of U.S. Pat. No. 5,887,799 are:
The impossibility to deliver both fuels at the same time.
The fuel rails are positioned at both ends of the injector, making installation difficult.
The need for a special injector driver that can reverse pulse polarity.
Other singlexe2x80x94injector designs utilized for dual fuel, liquidxe2x80x94liquid injection, rely solely on injector pulse signal modulation to accommodate for the different fuels. This technique is not applicable to most dual fuel, liquidxe2x80x94gas systems, where the energy density of the gaseous fuel is typically much lower than the liquid""s.
The device of the invention overcomes the aforementioned disadvantages of the prior art by utilizing a single fuel injector to supply two distinct fuels to an internal combustion engine. The injector is fluidically connected to two separate external fuel circuits, one for each of the two distinct fuels.
Each external fuel circuit comprises a fuel storage tank, a fuel pressure regulator and a fuel rail. In the preferred embodiment, the two fuel rails are coaxial, which makes packaging identical to a gasoline fuel injection system. Fuel access from the storage tanks to the fuel rails is controlled by an arrangement of valves. The two external fuel circuits are fluidically isolated from each other.
The injector has two separate internal fuel circuits, with at least one fuel flow control valve in each circuit. Each internal fuel circuit is fluidically connected to one of the fuel rails and isolated from the other fuel circuit.
In the preferred embodiment, the two fuel control valves are simultaneously driven by an electromagnet and feed of a desired fuel is achieved by selectively connecting one or the other of the fuel rails to the desired fuel storage tank.
Accordingly, Several Objects and Advantages of My Invention are
Ease of installation on the engine, since the fuel rails and injectors are similar in shape and size to the same components of a gasoline fuel injection system.
In the most common application, the conversion of a fuel injected gasoline engine to bi-fuel operation, on gasoline and a gaseous fuel, the fuel system of the invention does not entail any modifications of, or restrictions in, the engine intake air duct, thereby preserving the original gasoline engine performance and maximizing the performance potential for the gaseous fuel.
The fuel system, according to the invention, eliminates the need for a separate controller for the second fuel sub-system.
The possibility to run two distinct fuels simultaneously with one injector.
The possibility to use more than just two different fuels: i.e. compressed natural gas (CNG) and liquefied propane gas (LPG) could alternatively use the same railxe2x80x94but two distinct tanksxe2x80x94and the system would be a triple fuel one.
The fuel system, according to the invention, can be used for bi-phase, liquid or gas, LPG fuelling.